<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <title>title</title>
  <script>


    function F1(age) {
      this.age = age;
    }
    function F2(age) {
      this.age = age;
    }
    F2.prototype = new F1(10);
    function F3(age) {
      this.age = age;
    }
    F3.prototype = new F2(20);

    var f3 = new F3(30);
    console.log(f3.age);//


  </script>
</head>
<body>


</body>
</html>